mm/kasan: fix null pointer dereference warning in qlink_to_cache()

virt_to_slab() declared in slab.h can return NULL if the address does not
belong to a slab.  This case is not handled in qlink_to_cache() in
quarantine.c, which can cause a NULL pointer dereference in
"virt_to_slab(qlink)->slab_cache".  This issue was discovered by fanalyzer
(my gcc version: 12.1.1 20220507)

Link: https://lkml.kernel.org/r/20220626170355.198913-1-gautammenghani201@gmail.com
Signed-off-by: Gautam Menghani <gautammenghani201@gmail.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/kasan/quarantine.c b/mm/kasan/quarantine.c
index 75585077eb6dd46388ccdb05676aee7893dfc3d3..c7554f5b9fb6e8014e2142e6aa3f53520d12ccd2 100644 (file)
--- a/mm/kasan/quarantine.c
+++ b/mm/kasan/quarantine.c
@@ -128,7 +128,13 @@ static unsigned long quarantine_batch_size;
 
 static struct kmem_cache *qlink_to_cache(struct qlist_node *qlink)
 {
-       return virt_to_slab(qlink)->slab_cache;
+       struct slab *folio_slab = virt_to_slab(qlink);
+
+       if (!folio_slab) {
+               pr_warn("The address %p does not belong to a slab", qlink);
+               return NULL;
+       }
+       return folio_slab->slab_cache;
 }
 
 static void *qlink_to_object(struct qlist_node *qlink, struct kmem_cache *cache)